


under the covers

by kinkykawa



Series: youngblood (miyacest one-shots) [8]
Category: Haikyuu!!
Genre: (Brief) Vaginal Sex, Age Difference, Aged Down Atsumu, Alpha Miya Osamu, Alpha/Beta/Omega Dynamics, Alternate Universe - Canon Divergence, Breeding, Breeding Kink, Creampie, Dead Dove: Do Not Eat, If I Missed Something I'll Add It Later, Implied Mpreg, Incest, Intercrural Sex, M/M, Omega Miya Atsumu, Omegaverse, Sibling Incest, Somnophilia, afab language
Language: English
Status: Completed
Published: 2020-11-29
Updated: 2020-11-29
Packaged: 2021-03-10 03:41:05
Rating: Explicit
Warnings: Rape/Non-Con, Underage
Chapters: 1
Words: 1,957
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/27777790
Author URL: https://archiveofourown.org/users/kinkykawa/pseuds/kinkykawa
Summary: Atsumu keeps falling asleep in Osamu’s bed, and Osamu keeps letting him. Suddenly he doesn’t mind coming home every first weekend of the month, not if he gets to play with Atsumu like this.(Osamu decides that it's fine to have sex with his younger brother, and it's especially fine to do it while he's asleep.)
Relationships: Miya Atsumu/Miya Osamu
Series: youngblood (miyacest one-shots) [8]
Series URL: https://archiveofourown.org/series/1933474
Comments: 8
Kudos: 422





	under the covers

**Author's Note:**

> second of the de-aged omega!atsumu comms for [ceyri](https://twitter.com/osamyaatsum), this time with added somnophilia 👀 the given prompt was for osamu having sex with atsumu while he's asleep.
> 
> i mentally call this fic "how many ways can osamu badtouch atsumu in his sleep".
> 
>  **NOTE: please mind the tags.** the somno in this heavily straddles extreme dubcon to noncon territory, since atsumu is unaware (to osamu's knowledge) of what his brother is doing to him. i also **use afab language to describe atsumu's body** , although like the previous fic, i've opted not to tag this as trans male character. there are still indicators in the tags, tho! 
> 
> atsumu is thereabouts of 15-16 in this, while osamu is 19 and a freshman at university. i wrote most of this at 1am so if my english is questionable i'll fix it later. have fun; we are all sinners here.

Osamu means it to be just that one time.

He shouldn’t be doing anything at all, really, but it’s just too tempting. Atsumu napping in his bed because his younger brother has no sense of boundaries. Osamu knows it’s mostly instinct — an omega seeking a comforting and familiar alpha scent — but Atsumu _really_ needs to be more… _aware_ about these things. Such as the way he looks, sprawled on Osamu’s bed in his tiny shorts and a shirt he _definitely_ stole from Osamu. And the way he looks specifically to Osamu — to an alpha.

So yes, it might be more than a little wrong, but Osamu doesn’t think he can be faulted as he quietly, carefully closes his door. Atsumu’s a deep sleeper, won’t wake as long as Osamu doesn’t make too much noise. And there’s an omega in his bed, smelling cocoa-sweet, curled up and breathing softly.

Osamu softly drops his weekend bag to the floor, kicking it aside. Settles into his desk chair, turned to face Atsumu. Slowly unzips his jeans, pushing them down just enough to free his stiffening cock. Has to make do with spit, no lube left here after he’d packed up and left for university in Osaka.

Eyes fixed on Atsumu as he strokes himself fully hard, inhaling cocoa and sugar.

It feels incredibly perverse, which just makes it that much hotter. Atsumu makes quiet noises in his sleep every once in a while, little murmurs and soft exhales. Osamu bites his lip, squeezing his cock a little harder, flicking his thumb over the tip. There’s so much skin on display, his brother’s long legs, the strip of stomach where the shirt rides up. What would Atsumu do if Osamu were to reach out and touch him? Would he wake up, or would Osamu be able to touch uninterrupted, no need to come up with excuses?

(What would he do if he could touch — palms skimming up Atsumu’s thighs, cupping the curve of his ass; fingers creeping under Atsumu’s shirt, daringly close to pert nipples; inching Atsumu’s thighs open, little by little, pull his boxers aside or down—)

He comes with that visual, muffling a groan in his fist, cupping the head of his cock so he doesn’t make a mess. Not the first time he’s jacked off to Atsumu since his brother presented, won’t be the last, but certainly he’s never done it with Atsumu nearby. Osamu slumps back in his chair, chest heaving, quietly catching his breath. God he really hopes he packed a hanky somewhere accessible.

It’s so fucking tempting, after he’s cleaned up, tucked into fresh sweatpants and all evidence washed away. Atsumu’s _still_ asleep, although his nose is twitching slightly. In the end, Osamu sits at the edge of his bed, looming over his sleeping brother.

“‘Tsumu,” soft, sweet, brushing fingers over Atsumu’s cheek.

It’s frankly adorable, the way Atsumu blinks awake, brow furrowed. Makes it all the better when Osamu smacks a pillow in his face.

“Sleep in your own bed, you fucking brat.”

(He jacks off one more time later that night, face buried in sheets and pillows that still smell faintly of chocolate.)

_Just one time,_ he tells himself, but the next time he goes home — first weekend of every month, he’d promised — Atsumu is in his bed again. Osamu’s trying to write a paper at his desk, while Atsumu is ostensibly studying on his bed. When Osamu checks, though, his brother is fast asleep.

Carefree high schoolers. Honestly.

He shouldn’t, he _really_ shouldn’t, but it’s too damn enticing. Scoots his chair over by the bed, already palming his cock through his sweats. This time he dares — careful, light, reverent — to touch, trailing his fingers up the back of Atsumu’s calf. His brother is on his stomach, one leg lifted slightly. All the easier for Osamu to move higher, brushing the taut skin of Atsumu’s thigh, skirting the bruise on the side of his knee. His hand tightens around his cock when Atsumu makes a soft noise, Osamu’s fingers teasing near the seam of his thigh. Creeps into Atsumu’s loose shorts, brushing a knuckle over black underwear—

“Mnn.” Atsumu shifts, legs spreading a little wider. Osamu bites his lip and fucks against his hand harder. Strokes so, so lightly, feeling the warmth of his brother’s cunt through the fabric. Imagines what it would feel like to ease his fingers into tight, wet heat, or better yet, his _cock._

“ _Fuck._ ” Osamu shudders, shamelessly coming in his sweatpants as he presses two fingers over Atsumu’s clit. The air smells like coffee and chocolate; Atsumu’s underwear is a little damp. Osamu withdraws his hand, touches his fingers to his mouth as he strokes himself through the little aftershocks.

He’s back in clean pants and at his desk when Atsumu jerks awake, crumpling several worksheets as he sits up, half-startled. Atsumu scowls as Osamu grins, unable to contain his laughter, balled-up scrap paper hitting Osamu’s head.

Sweet, oblivious brat. Osamu graciously doesn’t throw anything back as a thank you for the visual his dear baby brother had unwittingly provided.

It isn’t just a one-time thing, two-time thing. Happens every time Osamu comes home and Atsumu is in his bed for some reason. Steals his brother’s underwear one time to use for jacking off, cocoa scent all over the fabric. Pushes Atsumu’s shirt up another night, pinching lightly at his nipples. One time he’s particularly daring, easing Atsumu’s shorts off and kneeling between his spread legs, fucking his fist as he braces himself over Atsumu’s crotch.

At some point he’d stopped caring about what explanation he’d give if Atsumu woke up. Probably just convince Atsumu it’s a good thing, kiss him or worse to shut him up. He’s not above taking advantage of Atsumu’s omega status and he knows it. 

Atsumu keeps falling asleep in Osamu’s bed, and Osamu keeps letting him. Suddenly he doesn’t mind coming home every first weekend of the month, not if he gets to play with Atsumu like this.

Tonight Atsumu’s fallen asleep watching a movie in Osamu’s bed, borrowing his laptop while Osamu does problem sets. He moves the laptop aside, nudging his little brother onto his back. Deft fingers ease Atsumu’s thighs open, then slowly tug his shorts down. He hesitates briefly — can he, could he — then the boxers come off too, and Osamu gets a perfect view of his brother’s cunt. Small, pink, exposed; Osamu teases a finger at the edge, watching Atsumu twitch. Jerks himself off imagining how it would feel to sink his cock inside, to _knot_ Atsumu, fuck. He’d be so tight, would take Osamu so well, pretty little omega underneath him. Osamu would open him up carefully, take his time, _wreck_ his brother so good—

Doesn’t even think as he leans forward, pressing the tip of his cock to Atsumu’s cunt as he climaxes, covering slick folds with cum. Shivers at the thought of it _inside_ Atsumu, his brother’s not in heat but the _thought_ of it makes Osamu quietly groan.

One more photo for his collection, Atsumu with his legs spread, cunt painted sticky-white. Osamu gnaws at his bottom lip as he trails his fingers through the mess, holding his breath as he carefully eases _inside._ Fucks his own cum into his younger brother, pushing it in, smearing it over Atsumu’s folds. 

Then Osamu licks at his fingers, tasting bittersweet-salt and slick, thick on his tongue alongside Atsumu’s cocoa scent.

Equally careful to redress Atsumu, pressing a kiss to an inner thigh as he tugs the shorts back into place. Climbs off the bed so he can go wash his hands and put his laptop away. When Atsumu half-wakes as Osamu climbs into bed with him, he just shushes his brother and tells him _it’s fine, go back to sleep._

He falls asleep breathing in chocolate, warm and sated, one hand laid possessively over Atsumu’s stomach.

(Dreams about it, during the in-between times. Scrolls through his photos and videos while alone in his tiny studio apartment in Osaka, stroking his cock as he remembers how Atsumu feels under his touch. Imagines he can smell chocolate as he comes, spurting into his fist, wants so desperately to come _inside_ Atsumu. Fuck a knot into him, stuff him full, he’d look _so_ pretty all messed up and all for Osamu. Only for Osamu.)

He finally crosses the line the next time Atsumu spends the night in his bed. Fell asleep there again watching in Osamu’s laptop; he won’t even question why his brother finds it more comfortable staying in Osamu’s bed instead of his own. Holds off this time, finishing up tonight’s schoolwork before he slides under the covers behind Atsumu. Far too trusting, no one questioning a young omega in an older alpha’s bed. Works to Osamu’s advantage, though.

He waits, hides his time scrolling through his phone, waits until Atsumu’s clearly deep asleep. Eases Atsumu’s shorts and underwear down — not all the way, just down to his knees so his thighs are trapped together. Osamu is prepared this time, packet of lube in hand. Rips it open and spills it on his hand, then slowly fits it between his brother’s thighs to slick them up. Brushes not-so-accidentally against his folds a few times, circles his clit. Then Osamu brings out his cock, coating it with the last of the lube until he’s fully hard.

It’s _heaven,_ slipping between Atsumu’s thighs, rubbing right against his slit. Not as tight as it would be if he were awake, or if Osamu could hold his legs shut, but more than enough as Osamu starts slowly rolling his hips. 

He’s determined to make this last, moving in short, shallow thrusts. Buries his face in his brother’s hair, smelling mint shampoo and his ever-present cocoa scent. Wriggles one arm under Atsumu to wind around his waist, hold him still. His free hand clutches at Atsumu’s hip. 

It’s good, so good, took a long while to work up to this but it’s worth the wait. Has to fight to keep quiet, soft panting against the back of Atsumu’s neck. So close to his scent gland, it’d just take a bite, Atsumu would be _his_ — but no, no. Not now. Can’t, not that. This is enough, tip of his cock rubbing at Atsumu’s clit with every thrust, his brother whimpering softly in sleep. Cocoa and coffee mingling in the air, so intoxicating Osamu feels dizzy from it.

His thrusts start getting more erratic the closer he gets to the edge. His cock teases against Atsumu’s entrance, tempting, wet heat waiting for him. Gives in right as he tips over, shoving the first few inches of his cock into Atsumu, teeth digging into his bottom lip as he comes. He won’t pop a knot like this, but it’s fine, fuck it’s _so good,_ feels like Atsumu’s sucking him in, so wet from Osamu rubbing against him. Spills into Atsumu like that, desperately holding his hips still, no matter that he wants to sink down to the hilt to make sure it _takes._

He’s barely caught his breath when he pulls out, tucking himself back in quickly. Dares to press his nose to Atsumu’s scent gland as he slips his hand between Atsumu’s thighs, swiping at the cum leaking out of him and pressing it all back inside. Gently, slowly, _playing_ with Atsumu as cocoa fills his lungs. When he’s satisfied, he carefully wipes the stickiness off his brother’s skin and pulls his clothes back into place. Kisses Atsumu’s hair and hums, content.

Can’t wait until the next time he’s back home for a weekend. There’s more he wants to do, and maybe at one point, Atsumu will be awake for it. One day.

**Author's Note:**

> WEW ALL RIGHT. i'm on twitter as [@kinkykawa_](https://twitter.com/kinkykawa_) if you guys wanna say hi and chat with me about more problematic content or just read my occasional OH SHIT TWINCEST HOT tweets 👀


End file.
